Glazed refractory article.



ductivity than porcelain.

sTaTTs TaTTNT oTTTo ARTHUR T. MALM, OF WORCESTER, MASSACHUSETTS,ASSIGiTOR TO NORTON COMPANY,

OF WORCESTER, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS.

GLAZED REFRACTORY ARTICLE.

No Drawing.

following is a specification.

This invention relates to glazed refractory articles having a base ofpreviously molten alumina, the object of the invention being to providea crucible or other article of this character which will withstandtemperatures to or above a white heat, while ossessing a far higherthermal con- Such articles are also more durable than the best porcelainunder all conditions of use.

To manufacture articles of this character I prefer to proceed asfollows: Calcinecl bauxite or other impure commercial form of alumina,or pure or purified alumina prepared by chemical'methods, is fused in anelectric furnace, and the product is crushed to gram and graded in theknown manner as practised for the manufacture of abrasive articles. Thisproduct is hereinafter referred to as alumina grain. The grains arepreferably then roasted in an oxidizing atmosphere in order to eliminatetraces of carbids or other reduction products which if present in thefinished article might cause local disintegfation 0r pitting of thebody. The grain is then mixed with a small pro-portion,

usually from five to fifteen per cent., or

somewhat more, of a flElastic clay, which serves as a bond, and so cientwater to produce a thin slip or body of suitable consist-- absorptivemold or form, which may be made of plaster of Paris. This mold or formtogether with the refractory coating is then dried at moderatetemperatures, say about 50 0., after which the article may be separatedfrom the mold, and will be found sufliciently strong to endure firing.

The molds or forms may be used an indefinite number of times. The firingis accomplished in kilns under standard conditions and at temperaturessufiiciently high.

' to fuse, vitrify or in some instances to partially vitrify the bond,as may be required Specification of Letters Patent. I

Patented Dec. 16, 1913.

Application filed May 29, 1912. Serial N 0. 700,468.

by porosity or other characteristics desired in the body.

The resulting article is very refractory and possesses a high degree ofporosity, being in both respects well-adapted to receive and retain aglaze. It is found however that the article has a relatively highcoeflicient of expansion at temperatures below a white heat, and it isnecessary to use a glaze of which the coeflicient of expansion so nearlyapproximates that of the refractory base that the glazed article may becarried through the entire range of temperatures below a white heatWithout checking, scaling or other injury to the glaze. A porcelaiuicglaze compounded as follows has however been found highly satisfactory:I

- A lead glaze compounded as follows may also be used:

. Feldspar 26. 37 per cent.

Whiting ((33,00 14. 38 1 White lead '12. 37

Clay 12.37

Flint 34. 51

These compositions may be melted and the refractory article coated bydipping; or the coating may be applied in anyapproved manner. In thecase of thin walled articles of high porosity the glaze may completelypenetrate the Wall, or it may be limited to the outer portions of thewall.

Crucibles and other articles prepared as above resemble glazed porcelainin appearance, but are far more serviceable and durable under conditionsof use. 'Pr'eviously molten alumina has a thermal conductivity more thandouble that of porcelain, andthis not only permits quicker and moreeconomical heating through alumina walls than through walls ofporcelain-but ver greatly reduces the strain set up in the wal s duringheating or cooling. However, the high thermic expansion of previouslymolten alumina renders it quite impossible to use ordinary potteryglazes with satisfactory results; and so far as I am aware it has neverbeen possible, prior to my invention, to provide an article consistingessentially of previously molten alumina and a bond with a glazedsurface capable of withstanding without injury rapidly succeedingextremes of temperature.

My invention is not limited to the specific glazing compositions aboveset forth, for the proportions of the several ingredients may besomewhat varied; and it is moreover possible that glazes may beotherwise compounded which will so closely approximate the thermalexpansion of previously molten alumina as to render them suitable foruse therewith.

Among the many articles which may. be prepared in accordance with thisinvention may be mentioned crucibles for laboratory use or for themelting of metals; combustion tubes and boats; spark plugs; variousforms of insulators for electrical purposes, etc. It will be understoodthat the article may be completely or only dpartially glazed, as itsintended use may in icate.

I claim:

1. As a new article of manufacture, a crucible or other articleconsisting of a body portion comprising alumina grain and a ceramicbond, and a porcelainic glaze for said body portion, the coeflicientvexpansion of said glaze closely approximating that of the body portion.

2. As a new article of ma ufacture, a crucible or other article consistig of a body portion comprising alumina grain and a ceramic bond, and aglaze for said body portion, the coeflicient expansion of said glazeclosely approximating that of the body portion.

In testimony whereof, I aflix my signature in presence of two witnesses.I ARTHUR T. MALM.

Witnesses:

CHAS. R.-MILLER, H. O ANDERSON.

